Full throttle AFR leans out after a few pulls, HELP!!!

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Full throttle AFR leans out after a few pulls, HELP!!!

Postby wendy-lad » Tue Feb 23, 2021 9:40 am

Hey guys,

Been having a recurring problem with a tune on a turbocharged 304 vr commodore where it runs perfect under load for about 3 or 4 full throttle pulls, then decides to start running lean for some reason..

So basically I'll hop in and start driving somewhere, about 10 mins later I'll start hitting boost and give it a bit of a squirt a few times, then cruise for another couple minutes, then give it another squirt and still runs fine. Then, say I'm about 20-30 minutes into driving, my next full throttle pull will read lean...

It's going from around 11.2ish consistently for the first bunch of pulls, then next pull will show 12.6 and be knocking cause it's so much leaner...

I've checked over my fueling system and nothing looks like it's out of the ordinary... I only started having this problem after the car was parked up for 6 weeks without moving.

I've replaced the fuel pump twice, ran new wiring and relays to the fuel pump, checked the resistance of the injectors hot vs cold, and nothing seems like it's out of whack, so I'm a bit unsure of what to check next.

I'm starting to lean towards the fuel pump that's in it is right on its HP limit, (it's a raceworks 320LPH) so possibly it works for a bit, then gets major heatsoak and craps out until I park up and let everything cool down for a bit?

Or is there something magical working in the background of the tune that's throwing things out?

Both normal and lean readings show the same charge and coolant temps, same MAP, same everything except duty cycle and injector BPW. Though in the tune it's still running the exact same VE numbers...

Has anyone seen this before, or has any idea on what to check or suss next?

Any input would be greatly appreciated.

Thanks

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby Gareth » Tue Feb 23, 2021 9:48 am

Sounds like a mechanical issue with the fuel system.

Need to get a fuel pressure guage on it and see what is happening. Has it still got the stock fuel pressure reg?
According to chemistry, alcohol is a solution...

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby wendy-lad » Tue Feb 23, 2021 10:52 am

Hey Gareth,

The stock fuel pressure regulator and dampener is gone, it's got a cheap Autobarn SAAS rising rate regulator which I've already swapped out for the same and didn't change anything.

We're sorta already guessing and realising that the fuel pressure is dropping when it starts running lean, just clueless as to why it's only after 20 or 30 minutes worth of driving and a few pulls...

I thought it couldn't be sucking the swirl pot dry or a mechanical issue as it only comes on after a bit of load, unless the heated fuel temp after a certain amount of run time is causing a mechanical issue?

Thanks

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby Gareth » Tue Feb 23, 2021 12:00 pm

I would also check the fuel pump current draw under load.
According to chemistry, alcohol is a solution...

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby wendy-lad » Tue Feb 23, 2021 12:50 pm

Hey Gareth,

That's another thing I didn't try but thought of, I just didn't want to muck around with extending a set of multimeter wires so I can see what it's drawing under load when everything's working properly vs not working properly...

I just ran all new wiring and a relay to the fuel pump, just in case it was a voltage drop under load once everything got some heat in it, and it didn't change anything.

Is it worth checking out? Or for the time and effort should I just drop in a bigger fuel pump and assume that'll fix it?

Thanks

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby Gareth » Tue Feb 23, 2021 1:49 pm

Assuming is never the answer, testing is the only sure way to find any problem.

Guessing with new parts is expensive
According to chemistry, alcohol is a solution...

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby kojab » Tue Feb 23, 2021 3:51 pm

Make sure you are not using a paper filter or any filter that will restrict flow to the ENTRY of the fuel pump. This will cause the pump to get very hot and drop fuel pressure.
A gauze filter only should be used on the entry of a EFI fuel pump. Paper filter after pump is fine.

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby Chuff » Tue Feb 23, 2021 5:44 pm

wendy-lad wrote:Hey guys,

Both normal and lean readings show the same charge and coolant temps, same MAP, same everything except duty cycle and injector BPW. Though in the tune it's still running the exact same VE numbers...


I really am no expert but if everything's the same whether it's lean or not except duty cycle and injector BPW then wouldn't that indicate that some condition has been met in the tune and the tune is changing the duty cycle and injector BPW accordingly?

I may be way off the mark, but that's how we learn.

Chuff
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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby 'quipt4it » Tue Feb 23, 2021 11:35 pm

Hi Wendy-lad,
I think you have plenty of pump.
Based on calculators, 320 lph should see you into 770hp (eng). That would assume 10lb boost pressure (I didn't see what you are running), 55 PSI fuel pressure, and running gasoline.
Some report the bulkhead connectors on GM vehicles not being able to handle enough current. There are upgrades for these.
This is a good read, https://ls1tech.com/forums/fueling-inje ... ector.html
Obviously you wouldn't skimp on wire gauge etc.
I wouldn't cheap out on the regulator either :cash:
Also, I don't see the need for removing the dampener (if you're talking about the one on the fuel rail), they help even out pulsations in the line.

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Re: Full throttle AFR leans out after a few pulls, HELP!!!

Postby Dylan » Wed Feb 24, 2021 7:16 am

Just a thought to put out there, watch the intake and coolant temps between runs. Heat soak is a Killer especially when stationary. There's tables to allow for this that nearly always need adjusting.

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